Both ozone and particulates are among the six major “criteria” air pollutants controlled under the Clean Air Act National Ambient Air Quality Standards, which are enforced by the U.S. Environmental Protection Agency.

Air quality milestone

Ozone pollution is caused by a reaction of sunlight and the vapors emitted when fuel is burned and is a common problem in metropolitan regions, such as Pittsburgh. Major emission sources include motor vehicles and industrial plants, particularly those that burn coal.

The 8-hour annual average for ozone in the seven-county Pittsburgh Metropolitan Statistical Area fell to .072 parts per million in 2017, slightly lower than in the previous year, EPA data report.

But from 2015-2017, the region averaged lower concentrations – .070 parts per million, which is the current standard, said Jayme Graham, chief of the Allegheny County Health Department Air Quality Program.

That led to EPA to designate the region to be in attainment of the 8-hour ozone standard for the first time since it was set in 1997.

The improved ozone levels are mostly due to cleaner motor vehicle technology, and coal-fired power plants installing pollution controls, converting to natural gas or being closed.

Recent ozone data also reveal a curious phenomenon in Allegheny County. For the past two years, the highest concentrations recorded have shifted from Harrison Township downwind of the City of Pittsburgh to South Fayette along the Washington County border. Readings in South Fayette are regarded as a barometer of the quality of the air entering Allegheny County. “South Fayette is overtaking Harrison. We need to figure out why,” Graham said.

Stubborn problem

Fine particulate pollution known as PM2.5 is a different story. Levels of the pollutant have fallen since the early years of the 21st Century. But the region took a step backward in 2017, with the annual average rising to 13.4 parts per million, up from 12.8 a year earlier.

Moreover, the region still fails to comply with the current annual standard for the pollutant, which is 12 micrograms per cubic meter of air.

PM2.5 are particles created when fossil fuels are burned, such as coal. Their microscopic size enables them to travel deep into the lung and blood stream, making them particularly dangerous. The most prolific sources are coal-fired power and industrial plant emissions.

The 2017 annual level in the Pittsburgh MSA is the highest among the 16 Pittsburgh Today benchmark regions. It represents the highest level recorded by air quality monitors in the Pittsburgh region.

Last year, that reading was taken at the Liberty Borough monitor in Allegheny County, which records the air quality in the industrial corridor downwind of the US Steel Clairton coke plant along the Monongahela River.

The recent increase is likely due to several factors. “There is variability due to weather, but there are some problems with the sources in that area,” Graham said.

The coke plant in Clairton is the most prolific particulate source in the Mon Valley. The coke works has been subject to several consent orders and decrees that required it to take measures to reduce pollution after being found to have violated regulations.

Annual PM2.5 concentrations in the corridor are much lower than a decade earlier as a result of

Economic conditions, regulation, advocacy, technological advances and industry investment, including more than $600 million in upgrades at the Clairton plant, helped lower PM2.5 levels over the past 10 years. Yet, that stretch of river valley is still saddled with the distinction of being one of the most polluted corridors in the nation.

Last year, the county ordered repairs at three of the Clairton plant’s coke batteries, which are expected to take three years to complete. This year, the county raised the financial penalties levied against violators of air quality regulations.

Meanwhile, Graham said, the county is developing an EPA-required plan for taming particulates that will likely require emission sources to invest in additional controls.